1. Field of the Invention
The invention relates to an UV spectrometer for the measurement of spectral intensities in the wavelength range below 190 nm.
2. The Related Art
The UV spectrometer of this invention is equipped with a gas flushing apparatus fitted with a system for minimizing gas consumption. The apparatus is also constructed to prevent the formation of absorbing deposits on optical windows, more particularly on the radiation inlet side, and maintain the partial pressure of absorbing residual gas components at a negligible level. Furthermore, the apparatus according to the invention achieves stable measuring results over a long period of time.
Due to the optical absorption of radiation in the wavelength range below 190 nm by components of the air, spectrometers in vacuum vessels are operated with a residual gas pressure below 1 Pa mbar. Devices for maintaining low pressure within conventional spectrometers are normally quite expensive.
For the spectral range of the so-called vacuum UV, of course, UV-transparent flushing gases are used instead of evacuating the spectrometer to pressures in the range below 10 Pa. The known systems of gas flushing are based on a relatively high gas flow in the range of 30-300 1/h (U.S. Pat. No. 4,322,165), the gas used requiring a very high degree of purity. Similar flow systems with a gas consumption of 5-10 1/h are known from the published literature. for instance, see T. Nakahara and T. Wasa, Applied Spectroscopy, Vol. 41, 1238, 1978; and T. Nakahara, Spectrochim. Acta, Vol. 40B, 293, 1985.
High gas flows are needed to keep residual gases, that arise from desorption and leakage, at a low enough partial pressure. Voluminous pressure gas flasks for flushing renders difficult the practical handling of the apparatuses and is very expensive.
In prior art vacuum spectrometers, dissociation of residual gases contained in the spectrometer vessel has led to formation of absorbing deposits on UV-radiated optical windows and other optical surfaces. As a result, the stability of spectrometric measurements is limited and very expensive maintenance is required. An additional disadvantage of those vacuum spectrometers is the cost of the relatively technologically sophisticated mechanisms required to be built into the instruments to obtain the necessary medium-high vacuum.
Known gas-flushed spectrometers have a relatively high gas consumption of 50-100N m.sup.3 per annum at STP and their state of adjustment depends on the external air pressure.